The guiding of a cutting tool in the tube of a pneumatic hammer is achieved conventionally by the provision of grooves in the inner surface of the tube which are engaged by corresponding teeth formed on a tail of reduced diameter on the tool engaged in the tube.
However, excessive wear has been found in the grooves of hammers utilizing cutting tools of large diameter while additionally abnormal wear has been found on the teeth of the grooved portion of the cutting tool.
In order to overcome these disadvantages, one solution consisted of increasing the drive surface of the hammer with the cutting tool by increasing either the length or the height of the teeth of the cutting tool.
However, the increase of the length of the grooved portion of the cutting tool has the disadvantage of increasing the tail of the cutting tool, thus increasing the cost and fragility thereof.
Furthermore, it was found beneficial to provide a space between the teeth of the cutting tool and the corresponding grooves in the hammer in order to form escape channels for the compressed air from the hammer. However, if the wear of the teeth of the cutting tool and the grooves of the hammer is obtained by increasing the height of the teeth of the cutting tool, it then becomes impossible to utilize the space between the teeth of the cutting tool and the grooves of the hammer as escape channels. In effect, the increase in the height of the teeth of the cutting tool diminishes the section of the channels and produce a constriction of the hammer leading to an unfavorable reduction of speed.